This invention relates generally to current-in-the-plane (CIP) magnetoresistive sensors, such as giant magnetoresistive (GMR) sensors, and their fabrication. More particularly the invention relates to such a magnetoresistive sensor with a biasing layer for longitudinally biasing the magnetization of the ferromagnetic sensing layer.
The most common CIP GMR sensor is a spin-valve structure with two metallic ferromagnetic layers separated by a very thin nonmagnetic conductive layer, wherein the electrical resistivity for the sensing current in the plane of the layers depends upon the relative orientation of the magnetizations in the two ferromagnetic layers. The GMR sensor has high magnetoresistance at room temperature with generally low noise, making it a primary sensor for use as a read head in high density hard disk drives.
IBM""s U.S. Pat. No. 6,266,218 describes a GMR read head as shown in FIG. 1 (which is FIG. 7 of the ""218 patent), wherein one of the ferromagnetic layers (the xe2x80x9creferencexe2x80x9d or xe2x80x9cfixedxe2x80x9d layer 76) has its magnetization fixed, such as by being pinned by exchange coupling with an adjacent antiferromagnetic layer 74, and the other ferromagnetic layer (the xe2x80x9cfreexe2x80x9d layer 78) is free to rotate in the presence of an applied magnetic field in the range of interest of the read head. Interposed between the free layer 78 and fixed layer 76 is an electrically conductive nonmagnetic spacer layer 80, typically made of Cu. This read head also has a third ferromagnetic layer (the xe2x80x9cbiasxe2x80x9d layer 87) that provides longitudinal biasing of the free layer 78 so that its magnetization in the sensing or active region 79 of the read head is stabilized in a single-domain state with predominantly longitudinal magnetization orientation. The width of the active region 79 determines the magnetic trackwidth (xe2x80x9cTWxe2x80x9d) of the read head.
The sensor described in the ""218 patent relies on longitudinal biasing or stabilization of the free layer end regions by antiferromagnetic exchange coupling with the bias layer 87. This requires the formation of the ferromagnetic bias layer 87 in close proximity to the end regions of the free layer 78, but spaced apart from the free layer by a thin nonmagnetic conductive layer 83 (such as Ru) which mediates a strong antiferromagnetic or antiparallel exchange coupling between the free layer end regions and the bias layer. The nonmagnetic conductive layer 83, also called the antiparallel coupling (APC) layer, is typically ruthenium (Ru) with a thickness in the range of 0.6 to 1.0 nm. To properly define the active region 79, the bias layer must be removed from the central active region 79 of the device. This presents a difficult problem in the fabrication of the sensor. If the bias layer is deposited first beneath the free layer (as shown in the xe2x80x9ctopxe2x80x9d spin valve structure in FIG. 1 because the fixed layer is on top) and then patterned, the required magnetic properties of the subsequently deposited sensor layers will be unobtainable. If the bias layer is deposited last on top of the free layer (so as to form a xe2x80x9cbottomxe2x80x9d spin valve structure reversed from that of FIG. 1 with the fixed layer on the bottom) then it is necessary to pattern and remove the bias layer over the central active region 79, while preserving the desired ferromagnetic properties of the free layer in the active region 79. Generally, techniques for removal of the unwanted region of the bias layer, such as ion beam etching through a photoresist stencil, will not be sufficiently precise to remove the bias layer while leaving the free layer unaffected.
What is needed is a GMR sensor that provides the same type of free layer longitudinal bias stabilization through antiferromagnetic exchange coupling of the free layer end regions, but by a more reliable manufacturing process.
The invention is a CIP GMR spin valve sensor that has its free layer magnetization stabilized by longitudinal biasing through the use of free layer end-region antiferromagnetic exchange coupling. An APC layer, such as Ru, is formed on the free layer and a ferromagnetic bias layer is formed on the APC layer. The bias layer is a continuous layer that extends across the entire width of the free layer. However, the central region of the bias layer is formed of nonmagnetic oxides of one or more of the elements making up the bias with the bias layer end regions remaining ferromagnetic. The oxidized central region of the bias layer defines the central active trackwidth region of the device. The ferromagnetic end regions of the bias layer are antiferromagnetically coupled across the APC layer to the corresponding underlying free layer end regions to provide the longitudinal biasing.
For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures.